This section is intended to provide a background or context to the invention recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this Application and is not admitted to be prior art by inclusion in this section.
The present description relates generally to a refrigeration system primarily using carbon dioxide (i.e., CO2) as a refrigerant. The present description relates more particularly to a CO2 refrigeration system with a direct CO2 heat exchange subsystem for heating and/or cooling a building or building zone.
Refrigeration systems are often used to provide cooling to temperature controlled display devices (e.g. cases, merchandisers, etc.) in supermarkets and other similar facilities. Vapor compression refrigeration systems are a type of refrigeration system which provides such cooling by circulating a fluid refrigerant (e.g., a liquid and/or vapor) through a thermodynamic vapor compression cycle. In a vapor compression cycle, the refrigerant is typically (1) compressed to a high temperature high pressure state (e.g., by a compressor of the refrigeration system), (2) cooled/condensed to a lower temperature state (e.g., in a gas cooler or condenser which absorbs heat from the refrigerant), (3) expanded to a lower pressure (e.g., through an expansion valve), and (4) evaporated to provide cooling by absorbing heat into the refrigerant.
CO2 refrigeration systems are a type of vapor compression refrigeration system that use CO2 as a refrigerant. It is difficult and challenging to adapt a CO2 refrigeration system to also provide heating or cooling for a building space. Typically, the CO2 refrigeration system is used to heat or cool an intermediate heat transfer fluid (e.g., water) which is circulated to the building and used to provide heating or cooling for air within the building space.